The primary aim is to investigate the mechanisms by which information about the sensation of itch is transmitted, and modified, by the central nervous system. Earlier investigations have provided evidence that in the peripheral nervous system the polymodal nociceptor population is involved in encoding the sensation of pruritus. There is no evidence that other known cutaneous receptor populations respond significantly to pruritogens or that there exists an unknown receptor population that signals itch. Since polymodal neurons respond to stimuli that produce pain, as well as itch, and thus are thought to encode information also about pain, experiments are planned to investigate how the sensory channels that signal pruritus are separated from those that signal pain within the spinal cord and to quantitate how these channels differentially respond to a variety of stimuli such as warm or cool temperatures (as well as noxious heat or cold), light or noxious mechanical stimuli, and substances (e.g., cowhage) or chemicals (e.g., histamine) that produce pruritus. In addition, there is psychophysical evidence that interactions occur within the central nervous system between itch and other sensory modalities. Experiments are planned to record from pruritogen-responsive neurons and determine how their behavior is modified by other types of stimuli delivered either inside, or outside, the neuron's receptive field. Psychophysical experiments are also planned to extend earlier observations. Initially, experiments will center on the behavior of relays within the spinal cord. Our longer-term goal is to investigate the processing of information about pruritus in higher order relays within the central nervous system.